Pivot base securing method and means



Dec. 11, 1962 A. T. SONATORE 3,

PIVQT BASE SECURING METHOD AND MEANS Filed May 9, 1960 ANTHONY Z SONA TORE IN VEN TOR.

United States Patent Ofifice 3,558,413 Patented Dec. 11, 1962 3,068,413 PIVQT BASE SECURING METHGD AND MEANS Anthony T. Senators, Holmdel, NJ, assignor, by mesne assignments, to Daystrorn, Incorporated, Murray Hill, NJ a corporation of Texas Filed May 19%, der. No. 27,574 3 Ciairns. (Cl. 324-155) This invention relates to an electrical instrument and more particularly to a method and means for securing the ends of a movable coil winding to the pivot bases attached to the coil.

Electrical instruments such as ammeters, voltmeters, and the like, include a wire-wound movable coil which coil may be wound upon a generally rectangular-shaped coil frame. Two pivot assemblies, each including a base and a pivot pin mounted on the base, are secured to the outer sides of the opposite ends of the coil, with the pivot pins projecting outwardly along an axis extending through the center of the coil. The pivots are carried in suitable bearings for pivotable support of the coil.

In a typical moving-coil mechanism, a pair of spiral springs are employed to provide a calibrated force 0p posing the moving coil torque; one spring surrounding each pivot base and connected thereto through suitable spring abutment members secured to the said pivot bases. The outer ends of the spiral springs are secured to outer abutments and, in accordance with established practice, the springs not only bias the moving coil to a predetermined zero position, but also are employed to conduct current to the coil; the ends of the coil windings being electrically connected to the pivot base to provide an electrical connection from the coil through the said spiral springs to the outer spring abutments. My invention includes a novel method and means of securing the ends of the movable coil windings to the pivot bases. In accordance with my invention, the end of the coil winding is secured to the pivot base simultaneously with the attachment of the pivot base to the coil. Further, in accordance with my invention, the end of the coil winding, or

coil lead, is secured to the bottom surface of the pivot base intermediate the pivot base and coil end turns. In a co-pending patent application Serial Number 23,228, now abandoned, of Raymond G. Drewes and Wallace W. Macintosh, filed April 19, 1960, and assigned to the same assignee as the present application, a method and means for securing a pivot base to an instrument coil are shown, which may be employed in the practice of this invention. The disclosure of such co-pending application is incorporated herein by reference thereto. Disclosed therein is a resistance heating method wherein an electrical current is passed through the pivot base to heat the pivot base and adjacent cement used in securing the base to the coil thereby at least partially curing or polymerizing the cement. With my invention, the bottom surfaces of the pivot bases and the ends of the coil winding are pre-tinned prior to securing the pivot base on the coil. The end of the coil is placed beneath the pivot base in contact therewith and the subsequent heating of the pivot base in securing the same to the coil also functions to solder together the pre-tinned base and coil lead.

An object of this invention is the provision of a method of soldering the end of a coil winding to a pivot base which method includes placing the pro-tinned winding end under the pre-tinned bottom of the pivot base and heating the pivot base to thereby solder the coil wire to the base.

An object of this invention is the provision of a moving coil assembly comprising a wire wound coil and a pivot base assembly secured thereto, and means soldering the coil wire end to the bottom side of the pivot base intermediate the pivot base and coil.

An object of this invention is the provision of a method of electrically connecting a coil wire end, by soldering, to a pivot base at a point intermediate the pivot base and coil.

An object of this invention is the provision of a moving coil assembly comprising a pivot base secured to a moving coil, and means soldering the coil end to the bottom surface of the pivot base intermediate the said base and coil.

These and other objects and advantages will become apparent from the following description when taken with the accompanying drawings. It will be understood that the drawings are for purposes of illustration and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the appended claims.

In the drawings wherein like reference characters denote like parts in the several views:

FIGURE 1 is a side elevational view of a coil assembly embodying my invention, parts being shown broken away for clarity;

FIGURE 2 is an exploded fragmentary sectional view showing the connection between one end of a coil wire and a pivot base; and

FIGURE 3 is a fragmentary, semi-diagramm-atical view of a positioning fixture with a coil assembly mounted thereon, which fixture may be used in the method and means of soldering the end of the coil winding to the pivot base in accordance with my invention.

Reference is now made to FIGURE 1 of the drawings wherein there is shown a coil assembly comprising a generally rectangular-shaped coil frame lil with a wire wound movable coil 11 wound thereon. A pivot assembly comprising a pivot base 12 and a pointed pivot 13 is mounted at each end of the coil, which pivots are shown rotatably supported in jewel bearings 14.

The pivot base may comprise a flat base portion 16, an upstanding rectangular boss 17 and an externally-threaded cylindrical portion 18, the latter having an axial bore, not shown in FIGURE 1 for accommodation of the pointed pivot 13. A piece of insulating material 19, of cloth or paper, or the like, is positioned between the coil 11 and base portion 16 of the pivot base to serve as insulation therebetween. Suitable cement secures the pivot base and insulating member to the coil winding, as described in detail hereinbelow.

A conventional pointer 21 with a hub portion having a hole therein is mounted on the pivot base, the cylindrical portion 1% of the base extending through the hole with the pointer hub resting on the boss 17. A washer 22 is located between the pointer 21 and an inner spring abutment 23. At the lower end of the coil assembly the spring abutment 23 abuts the boss 17; no pointer being included at that end. Nuts 24 threaded on the externallythreaded portion 18 of the bases secure the pointer and inner abutment thereto.

The inner ends of spiral springs 26 are secured to the abutments23, while the outer ends of the spiral springs are mounted on relatively fixed outer abutments 27 fragmentarily shown in FIGURE 1. In accordance with established practice, the spiral springs not only bias the coil to a predetermined position, but also provide a conducting current path to the coil. Lead wires: 28 are shown secured to the abutments 27 for connection to a source, not shown, to be measured. The current path from the lead wires 23 may be traced through the spiral springs 26, abutments 23, and pivot bases 12 to the ends of the coil winding which are soldered to the pivot bases in a novel manner in accordance with my invention.

Reference is now also made to FIGURE 2 of t -e drawings showing an exploded view of a joint between a coil and pivot base. For clarity, the parts and elementsof the connection have not been shown in proper relative size; the drawing being intended merely to aid in an understanding of the invention. in securing the pivot base to the coil, a thin layer of suitable cement 33 is first brushed onto the end turns of the coil 11 and the insulating member 1% is placed in position thereon. A thin coating of cement, designated 32, is then spread over the insulating member. The end of the coil wire, designated 11', which who has been pro-tinned as at 33, is then placed on the insulating member 13 upon which the cement 32 has been spread. In accordance with my invention, the bottom surface of the pivot base is tinned, as at 3 before the base is placed on the insulating member 19 upon which the cement 32 and tinned wire end 1i. have been placed. With the pivot base positioned on the insulating member 19, in contact with tnc tinned wire end, heat is applied to the pivot base to simultaneously solder the coil lead to the pivot base and to set the cement. A suitable method and apparatus for properly locating the pivot base on the coil and of heating the pivot base to set the cement and solder the coil wire to the base are shown and described in the above-mentioned copending patent application Serial Number 23,228. A fragmentary, semi-diagrammatical, view of a means for locating the pivot base on the coil and including means for passing an electrical current through the base to heat the same is shown in FIGURE 3. In FIGURE 3, the coil 1% is shown positioned upon a pedestal 36 or" a positioning fixture. A plunger element 38, spring biased in the direction of the arrow designated 39 and comprising a portion of the positioning fixture, accurately locates the pivot base 12 on the end turns of the coil. A pair of electrodes 41, 41 are shown in contact with the pivot base at spaced points thereon, the said electrodes being connected through lead wires 42, 42 to the secondary winding 43 of a transformer $4. The transformer primary winding 46 is connected to a suitable A.-C. source 47 through a switch 4-3. As described above, a thin layer of suitable cement is applied to the coil, the insulating member 19 is placed thereon, a thin layer of suitable cement is applied to the insulating member and the tinned pivot base is placed thereon with the tinned coil lead in contact with the pivot base. The coil assembly is then placed in the positioning fixture to properly locate the pivot base (or both bases simultaneously) on the coil. With the electrodes 41, 41 in place on the pivot base, the switch 48 is closed and an electric current is passed through the said pivot base. A current ilow of 20 amperes for about 0.5 second has been found to provide the necessary amount of heat to properly gel one particular epoxy resin type cement. The heat thus provided simultaneously solders the tinned wire end 11 to the bottom tinned surface of the pivot base and gels, or cures, the cement sufliciently to keep the pivot base in place on the coil.

With the coil lead 11 positioned beneath the pivot base, my invention is particularly applicable to an arrangement wherein the coil wire is of a small size since a large wire would possibly permit rocking of the pivot base thereon. In one application, a coil wire of .061" diameter is used with an insulating member 1? having a thickness of .003, which Wire is sufficiently small to embed in the cement and insulating member to thereby permit a stable mounting of the pivot base on the coil.

It will be understood that my invention is not limited to any particular type cement since any suitable heat reactive cement may be used. The cement may be of the thermoplastic or thermosetting type. VJith certain heat reactive cements and with sufficient heat provided by the current flow through the pivot base, the cement may be finally gelled or cured without further baking. With other cements, a further oven baking subsequent to the above-described resistance heating process may be required. Obviously, both pivot bases may be simultaneously secured to the movable coil, at the same time both coil leads are being soldered to the pivot bases. Since the soldering of the coil lead to the pivot base and the securing of the said pivot base to the coil are simul taneously efiected, it will be apparent that the prior art step of soldering the coil leads to the pivot bases after the pivot bases are secured to the coil is eliminated. Further, the resulting soldered connection is superior to prior art arrangements since the contact is embedded in the cement and no corrosive effects of the atmosphere therein take place.

Having now described my invention in detail in accordance with the requirements or" the patent statutes, various other changes and modifications will suggest themselves to those skilled in this art and it is intended that such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.

I claim:

1. A method of manufacturing a movable coil as sembly of an electrical instrument of the movable coil type and which includes a wire-wound movable coil with loads and a pivot base secured to the coil, the said method including tinning the coil leads and the bottom surface of the pivot base, spreading a heat reactive cement on the coil, placing an insulating member on the cement, spreading a heat reactive cement over the insulating member,

a pivot base secured to the coil, the said method including tinning the coil leads and the bottom surface of the pivot base, spreading a heat reactive cement on the coil, placing the bottom surface of the pivot base on the cement spread on the coil with the tinned wire lead in contact with the tinned bottom surface of the pivot base, and heating the pivot base thereby gelling the cement and soldering the coil lead to the pivot base.

References Cited in the file 6r this patent UNITED STATES PATENTS 2,425,443 So-reng Aug. l2, 1%!

2,735,068 Wolferz Feb. 14, 1956 2,890,416 Walker June 9, 1959 2,953,673 Bouton Sept. 20, 1960 FOREIGN PATENTS 576,801 Great Britain Apr. 18, 1946 OTHER REFERENCES Publication, Selectacon, Engineering Bulletin No. 9, by Tape Cable Corp, Rochester, N.Y., November 1958. 

